1) Field of the Invention
The present invention relates to a liquid crystal display device using an illuminating device constituted of a rod-shaped light transmission body and a planer light transmission body, and in particular to a rod-shaped light transmission body having a plurality of prisms.
2) Description of the Related Art
Recently, a liquid crystal display element and a liquid crystal display device used in an information terminal are required to provide high display quality such as colorization, high luminance, or high resolution. Since the liquid crystal display element is thin and light, it is widely used as a display unit for a portable type information terminal.
FIG. 11 is a sectional view showing a conventional transmission type liquid crystal panel. As shown in FIG. 11, the transmission type liquid crystal panel has a polarizer 214 interposed between a glass base plate 210 and a glass base plate 212. A bus line or the like is formed on the glass base plate 212. Liquid crystal 220 is sealed between the glass base plate 212 and a glass base plate 218. Further, a color filter 224 is interposed between the glass base plate 218 and a glass base plate 222. A polarizer 228 is interposed between the glass base plate 222 and a glass base plate 226.
In the transmission type liquid crystal panel, the color filter and the liquid crystal are sandwiched between the polarizers, and in a reflection type liquid crystal panel, the polarizer 214 is replaced by a reflecting plate such as a mirror. In each of the liquid crystal panels, when linearly polarized light passes through the liquid crystal, a phase thereof is modulated due to characteristics of the liquid crystal, and the modulated light passes through the color filter to pass through the polarizer or be reflected by the polarizer, thereby performing white and back display. Character information or image information is constituted by arranging a plurality of while and black dots. On the other hand, since the liquid crystal itself is a light receiving element that does not emit light, it is difficult to view the information in the liquid crystal alone.
In order to solve the problem, an illuminating device as illuminating means is arranged on a back face of the transmission type liquid crystal panel or on a front face of the reflection type liquid crystal panel. Since the reflection type liquid crystal panel is illuminated by solar light or room light, an illuminating device is not required under such a condition. When the reflection type liquid crystal panel is not placed in an illuminating environment, an illuminating device like the transmission type liquid crystal panel is required. The illuminating device includes a point light source, a rod-shaped light transmission plate, and a planer light transmission body. Therefore, light emitted from such a point light source such as a LED is converted to a line light source by the rod-shaped light transmission plate, light from the line light source is incident on the planer light transmission plate, and the incident light illuminates a whole surface of the liquid crystal panel.
Patent Literature 1 (Japanese Patent Application Laid-Open No. H7-325208) discloses a technique of a liquid crystal display device provided with a prism sheet having at least two apex angle portions, slants of respective prism portions thereof being formed curvilinearly, apex angles being formed by the curved portions, and angles of the apex angle portions being different from one another.
Patent Literature 2 (Japanese Patent Application Laid-Open No. H10-214035) discloses a technique of a back light device having a prism sheet including a plurality of triangular prisms with different apex angles, at least one of the apex angles being in a range of 80° to 100°, and a liquid crystal display device using the back light device.
Patent Literature 3 (Japanese Patent Application National Publication (Laid-Open) No. 2003-511735) discloses a technique of forming an optical film provided with a polarizing prism array formed on an input face thereof which is useful for reducing or avoiding ripples (non-uniformity of luminance).
Patent Literature 4 (Japanese Patent Application Laid-Open No. 2003-77326) discloses a technique of an illuminating device that is provided with a light source that emits light, and a linear light transmission body that reflects light introduced from the light source by a plurality of light reflecting portions formed on an opposed side thereof from the light source and linearly outputs the light from a side thereof opposed to the opposed side for obtaining even light intensity, where faces of the light reflecting portions are respectively inclined at such angles that light is converged in the eyes of a viewer.
In view of the above problems, it is an object of the present invention to provide a rod-shaped light transmission body that has a simple constitution and is realized with a low cost, an illuminating device that provides sufficient brightness using the rod-shaped light transmission body, and a liquid crystal display device using the illuminating device.